1. Field of the Invention
An organic light emitting diode (OLED) display having a photo sensor that detects an amount of external light, where an automatic luminance control function can be efficiently performed by increasing a condensing efficiency of the photo sensor.
2. Description of the Related Art
Flat panel displays, such as an organic light emitting diode (OLED) display or a liquid crystal display (LCD), are recent displays. The OLED display has self-luminance characteristics, and the thickness and weight thereof can be reduced since a separate light source is not required. Further, because the OLED display has high quality characteristics such as low power consumption, high luminance, and high reaction speed, the OLED display is appropriate for use in mobile electronic devices.
The OLED display realizes a predetermined image in a display area where OLEDs are located. However, external light greatly influences display quality. Particularly, a screen contrast ratio is related to luminance of reflected light (external light reflected from the OLED display). The contrast ratio (CR) can be expressed as given in the following equation:CR=1+(Lself-emission/Lreflected light)
where Lself-emission denotes luminance of self-emission and Lreflected light denotes luminance of reflected light. As shown in the equation, the screen contrast ratio is inversely proportional to the luminance of the reflected light. Since the luminance of the reflected light is proportional to the amount of external light, the screen contrast ratio decreases when the amount of external light increases.
In order to solve this problem, an OLED display having an automatic brightness control function by using a photo sensor has been disclosed. The automatic brightness control function constantly maintains a screen contrast ratio by compensating luminance of self-emitted light according to the amount of external light by inputting an amount of external light detected by the photo sensor into a luminance controller.
The photo sensor is formed on a first substrate where OLEDs are formed, and is located external to the display area. In addition, a second substrate is bonded to the first substrate to protect the OLEDs and the photo sensor from the external environment, and a polarizing plate is attached to an external face of the second substrate for improving the screen contrast ratio.
However, when the polarizing plate covers an area where the photo sensor is formed, the transmittance of external light to the photo sensor is impaired due to the presence of the polarizing plate. This results in a decreased efficiency of the photo sensor. In addition, when the polarizing plate is attached to a display area in such a way as to not cover the photo sensor, irregular reflection can easily occur in a portion of the second substrate that corresponds to the photo sensor, so that the efficiency of the photo sensor can also be decreased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it can contain information that does not form the prior art as per 35 U.S.C. 102.